1. Field of the Invention
The present invention is related to fluidized bed reactors.
2. Problems to be Solved
Fluidized bed reactors are typically used to process waste or sewage. One type of conventional fluidized bed reactor incorporates a self supporting refractory brick arch or dome located below the fluidized bed. As used herein, the term "refractory" is defined as materials of the ceramic type, such as pre-fired clay. The refractory bricks are fitted with tuyeres to distribute gas to the fluidized bed. One problem with this type of reactor is that the weight of the refractory brick arch, and the weight of the bed when not fluidized, as well as the thermal stresses induced in the arch during operation, can impose large horizontal and radial forces on the reactor shell or walls. As such, it is the conventional practice to place a metal band, known as a "belly band", around the reactor to help contain the forces. However, the load carrying capability of the band is limited by size and material restrictions. Another problem is that the maximum size of the refractory brick arch, and therefore the maximum processing area, is limited by the load carrying capabilities of the bricks. When a certain diameter is attained, the arch will no longer be self supporting. Thus, the maximum achievable arch or dome diameter limits the diameter of the reactor. A further problem is that the refractory brick arch is pressurized with gas which passes through the tuyeres. The gas differential pressure across the tuyeres results in pressure on the refractory arch or dome. This pressure tends to lift the arch which is kept in its normal position by the weight of the arch or dome. Thus, such a problem limits the maximum allowable pressure of gas distributed by the tuyeres. Thus, the maximum achievable size of the arch bricks or the dome limit the maximum achievable pressure drop across the tuyeres. Furthermore, the gas distributed by the tuyeres tends to escape through any crevices or spaces between the bricks of the arch and enters the fluidized bed.
Another type of fluidized bed reactor incorporates metallic plates or dished-metal heads instead of a refractory brick arch. One problem with this type of reactor is that the maximum reactor diameter is limited by the maximum available size of the dished-head. The size of the dished-head is limited by acceptable stresses and expansions produced by variation in temperatures. Furthermore, as a consequence of warping and deformation resulting from the high process temperatures, it is difficult to ensure free expansion of the dished-head, as well as the integrity of mechanical seals as the gas differential pressure across the tuyeres increases. This problem becomes more acute as the size of the dished-head increases.
Bearing in mind the problems and deficiencies of conventional fluidized bed reactors, it is therefore an object of the present invention to provide a new and improved fluidizing gas distribution system for a fluidized bed reactor that does not limit the size of the fluidized bed reactor.
It is another object of the present invention to provide a new and improved fluidizing gas distribution system that can withstand relatively high pressure drops across the tuyeres.
It is a further object of the present invention to provide a new and improved fluidized bed reactor that substantially eliminates leakage of fluidizing gas into the fluid bed.
It is another object of the present invention to provide a new and improved fluidized gas distribution system that can freely expand and contract within a fluid bed reactor in response to variations in pressure and temperature within the reactor.